Today, access to the Internet is available to a wide audience through the public switched telephone network (PSTN). Typically, in this environment, a user accesses the Internet though a full-duplex dial-up connection through a PSTN modem, which may offer data rates as high as 56 thousand bits per second (56 kbps) over the local-loop plant.
However, in order to increase data rates (and therefore improve response time), other data services are either being offered to the public, or are being planned, such as data communications using full-duplex cable television (CATV) modems, which offer a significantly higher data rate over the CATV plant than the above-mentioned PSTN-based modem. Services under consideration by cable operators include packet telephony service, videoconference service, T1/frame relay equivalent service, and many others.
Various standards have been proposed to allow transparent bi-directional transfer of Internet Protocol (IP) traffic between the cable system headend and customer locations over an all-coaxial or hybrid-fiber/coax (HFC) cable network. One such standard, which has been developed by the Cable Television Laboratories, is referred to as Interim Specification DOCSIS 1.1. Among other things, DOCSIS 1.1 specifies a scheme for service flow for real-time services such as packet telephony. Packet telephony may be used to carry voice between telephones located at two endpoints. Alternatively, packet telephony may be used to carry voice-band data between endpoint devices such as facsimile machines or computer modems.
When real-time communication is to be established over a cable network, the network elements initially do not know whether the call will carry voice or voice-band data. While this is generally not a problem when the call is established over a public switched telephone network since sufficient resources are always available, in an HFC cable network bandwidth is shared. A goal of network operation is to limit the bandwidth requirements of any one call to allow more calls/subscribers to be supported. Accordingly, to reduce the bandwidth that is required, compressing codecs often are used with voice traffic. Such compressing codecs are not used with voice-band data because they do not reproduce the data with sufficient accuracy. Because compressing codecs can be used with voice but not voice-band data, the bandwidth required by voice-band data is greater than the bandwidth required by voice traffic. Since it is initially not known whether a connection is to support voice traffic or voice-band data, sufficient bandwidth must be allocated to support voice-band data. If it turns out that the connection is only to be used to support voice traffic, more bandwidth will have been allocated than is required, thus reducing the efficiency of the network.
Accordingly, it would be advantageous to modify the bandwidth allocated to a real-time packet switched connection over a cable network depending on whether the connection is to carry voice traffic or voice-band data. This applies particularly to cable network bandwidth in the upstream direction from the customer location to the headend, as this bandwidth typically is limited compared to the downstream bandwidth.